Foam producing units have long been known for extinguishing fire, or for spreading foam on airport runways to enable crippled planes to slide to a safe landing. However, such apparatus has usually consisted in an elongated fire crash truck constructed especially for the purpose at high cost.
Prior art units, for example as shown in U.S. Pat. No. 3,129,890 to Britton of Apr. 21, 1964, have been limited to one foam generating agent only such as protein, or aqueous film forming foam (AFFF), and therefore have either been able to instantly extinguish flame or smother the fire after extinguished but not both.
It is well known to introduce a chemical into water to fight fires as disclosed in the following U.S. patents relating to proportioning, mixing, eduction, venturi throats, or the like. Pat. Nos:
U.S. 2,567,997, Granberg, 1951; 2,934,149, Bedford, 1960; 3,115,158, Sheppard, 1963; 3,667,687, Rivkind, 1972; 3,388,868, Watson, 1968; 3,642,072, Livingston, 1972; 3,701,482, Sachnik, 1972.